There is known a droplet container that contains a liquid medicine such as eye drops and drips a drop thereof. Such a droplet container is generally provided with a check valve for preventing a backflow of a liquid medicine in view of hygiene.
Patent Literatures 1, 2, and 3 each disclose a check valve structure including a valve seat, a support, and a flat plate-shaped valve element supported therebetween. Each valve element is supported such that its center projects downstream (outside a container) from upstream (inside the container). Thus, when receiving pressure from upstream toward downstream, the valve element deforms such that its center projects further, and then fluid flows around the valve element. Meanwhile, when receiving pressure from downstream toward upstream, the valve element deforms so as to return to a flat state to close a passage.
Patent Literatures 4 and 5 each disclose a check valve structure including a valve element having a notch formed at its center. Thus, the notch at the center of the valve element opens when receiving pressure from upstream toward downstream, and closes when receiving reverse pressure. Patent Literature 5 also describes an effect of drawing back remaining liquid in a nozzle caused by returning of the valve element to the original shape.